1. Field of the Invention
This invention relates to the regulation of plant growth, and more particularly to the molecular cloning and expression of a gibberellin 20-oxidase gene and its use, for example in transgenic plants.
2. Description of the Related Art
Chemical compounds for control of plant growth have been in commercial use for many years. Many of these compounds act by inhibiting various steps in the biosynthesis of gibberellins (GAs). GAs form a large group of diterpenoid natural products, some members of which function as hormones in plants, controlling many aspects of development, including, for example, shoot elongation. Among the groups of compounds which inhibit GA biosynthesis in higher plants are quaternary ammonium and phosphonium compounds, compounds with a nitrogen-containing heterocycle, and acylcyclohexane-diones. However, the use of such chemicals involves several problems. It is, for example, difficult to apply the chemicals to plants in the appropriate quantities, or to select plant organs, without the chemicals spreading to other plants or animal life. There is a risk of persistence which can make it difficult to grow other crops subsequently to treated crops. A problem addressed by the present invention is therefore to avoid the use of such chemicals. This problem can be solved within this application by providing means for plant growth control at the plant gene level.
The later steps of the GA biosynthetic pathway are catalysed by soluble 2-oxoglutarate-dependent dioxygenases, several of which have been proposed as regulatory enzymes in the biosynthesis of the physiologically important C.sub.19 compound, GA.sub.1. For example, the activity of the GA 20-oxidase is enhanced by long days in certain photoperiod-sensitive plants and is down-regulated as a consequence of GA.sub.1 action in several species.